1. Field of the Invention
The invention relates to a method and an apparatus for heat treating a shaped member, particularly for hardening and/or scorching a friction lining of a brake or clutch lining.
2. Description of Related Art
Friction linings should exhibit a constant coefficient of friction to the greatest extent possible, even when they are first used. After its manufacture, however, an untreated lining generally has a decrease in its coefficient of friction when it is first loaded. Only after a certain running in time does the frictionally active surface of the lining carbonise so that the coefficient of friction stabilises.
Precisely when braking, a good braking action and a coefficient of friction which is constant over all loads is required from the very beginning for safety reasons. The friction lining is therefore frequently subjected to a post-treatment, which prevents so-called initial fading and stabilises the coefficient of friction.
It is known in practice to “scorch” friction linings after the grinding process. The lining is pressed against a hot plate at ca. 450° C. to 800° C. It is also known to flame the friction lining surface or to process it with laser beams or infra red light. As a result of the carbonisation of the friction lining surface, a friction lining is produced with a constant coefficient of friction. Linings pre-treated in this manner no longer need to be “braked in”. They are fully capable of use from the very beginning.
One of the disadvantages of the known methods is the low degree of efficiency of the heat treatment. The energy losses are considerable as a result of the unnecessary heating of the environment and regions of the brake lining, which require no heat treatment. The process is also time-consuming. Similar considerations apply to the hardening of the brake lining. After the pressing process, the brake lining is commonly hardened in a furnace. Energy losses occur in this case also as a result of the heating of material which is “not relevant”.